WaterproofHaving our drive be waterproof is a relatively obvious requirement even though USB disks tend to be relatively impervious to water just by themselves. If a cheaper drive gets wet it is generally just a matter of drying it out before using it again. The key word there, of course, is "generally". If you try to use a wet USB drive, get it wet with impure water which may cause deposits to form on the circuit board when the water evaporates, or even drop it in something other than water then your drive may not fare so well. I would like a drive so waterproof there would be no worry about getting it wet or dirty.
The other question in regards to waterproof is "how waterproof"? It is easy to mistake this for a binary "yes/no" question when in fact there are a number of standards such as IP and NEMA made to determine how water (and dust) proof an item really is. But even these are just the beginning: the highest typical IP rating is IP68 which only represents something being able to withstand continuous immersion in 1 m of water. Waterproof ratings beyond this are typically specified in how much pressure something can withstand over a certain period of time.
A quick calculation shows that for every 1 m underwater our pressure increases by 1.5 psi (10 kPa). In my previous job we would regularly make parts that were rated to at least 300 psi for use in water systems and other parts rated to 3000 psi for use in oil and gas, each typically rated at that pressure for at least several hours with no leaks. Exactly how high of a rating we need, or want, for our own USB drive depends mostly on how difficult it will be to achieve although ideally we'd like a pressure rating as high as possible.
Crush Resistant/RuggedThis is a particularly weak point of most USB drives out there. Cheap ones likely wouldn't survive being stepped on and even most metal cased ones wouldn't survive being run over by a car. In order to meet its namesake of a "virtually indestructible" drive we'd like our design to be as strong as possible without having to sacrifice any of its other requirements, especially its price. Ideally something that would just shrug off being run over by a large car or truck would be great.
Prevent Cap LossI simply can't stand USB drives that have a detachable cap with no method of storing it. Generally these caps only last around 27 seconds before they are lost in some unexplainable manner. In order to meet the "rugged" and "waterproof" requirements we will almost assuredly need a cap and so will also need a design to prevent the cap from being easily lost.
PriceMaking a VIUD would be relatively easy if price were no object. If we were just making a one of a kind drive then price would be mostly irrelevant but if we wish to market and sell these drives at some point (a fair assumption) then having something more affordable would be advantageous.
The price per drive can be roughly broken up into three categories:
- Case Manufacturing - Mass production can greatly decrease the price per unit.
- USB Drive Board - Buying something off the shelf in bulk would be ideal.
- Assembly - Something that minimizes the final assembly time would be good.
There is also the one time development costs, marketing, shipping, and hours spent on the project to consider to ensure that we don't lose money by making the drives.
This may appear to be a silly design requirement but making a good looking, or even beautiful, drive is important, particularly if we're interested in selling it is as a product.
I forgot about this design requirement initially although it may be one of the more important. We could easily make an indestructible USB drive by encasing it in a 10 kg brick of Titanium. This would more than satisfy all design requirements, except possibly the price, jowever, a 10 kg brick is not something you can drop in your pocket and use anywhere you would use a regular USB drive. Ideally we would want something very similar in size, shape, and weight to existing USB drives, or at least not too far away from.
So it seems our design requirements are complete even if some of them are in the "as rugged as possible" category. It will take some design testing and prototypes to determine exactly how much we can get.